1. Field of the Invention
The present invention is generally in the field of electrical circuits. More particularly, the invention is in the field of termination circuits.
2. Background Art
A termination circuit, such as a communications termination circuit or a memory termination circuit, typically provides a termination resistance to a common node, so as to prevent degradation of signal integrity on communications lines. Sometimes the common node is not at ground potential. Sometimes the common node voltage is at a potential half way between ground and a power supply voltage, and the required termination voltage is regulated in some manner. For example, a memory termination circuit, such as a double data rate (DDR) dynamic random access memory (DRAM) termination circuit can be required to provide a termination voltage approximately equal to one-half of a supply voltage, such as VDD, at the regulated voltage node. However, conventional termination circuits, such as conventional DDR DRAM termination circuits, suffer from various disadvantages.
In one conventional termination circuit, a plurality of communication lines are each driven by a driver and coupled to a regulated voltage node by a termination resistor and also coupled to a load. The regulated voltage node is coupled to a ground through a capacitor and also coupled to a termination voltage regulator, which is a special regulator that can source and sink current. Although the termination voltage regulator can provide a precise termination voltage at the regulated voltage node, the termination voltage regulator is a separate component that can undesirably increase manufacturing cost.
In another conventional termination circuit, a plurality of communication lines are each driven by a driver and each terminated with two resistors. Each communication line is coupled to a supply voltage, such as VDD, by one termination resistor and coupled to a ground by another termination resistor. The two termination resistors can, as a pair, provide a Thevenin-equivalent termination voltage of VDD/2. However, the additional termination resistor required at each regulated voltage node can undesirably increase manufacturing cost. Also, the conventional termination circuit can draw DC power through the termination resistors, which undesirably increases power consumption.